This article presents morphological descriptions of larvae and adults of Hypopygiopsis tumrasvini Kurahashi (Diptera: Calliphoridae), a blow fly species that may be of forensic importance. Both second and third instar larvae are illustrated, with emphasis placed on important characteristic features used for larval identification, such as the cephalopharyngeal skeleton, anterior and posterior spiracles, and dorsal spines between the prothorax and mesothorax. Eight to 11 papillae were found on each anterior spiracle arranged in a single row. The dorsal spines between the prothorax and mesothorax were arranged in sets of posteriorly projecting acuminate spines with darkly pigmented tips. The posterior spiracles each bear three prominent and separated long, slender spiracular slits encircled by a dark, thick peritreme that is complete ventromedially around a button. Prominent inner projection of peritreme is seen between the middle and lower spiracular slits. A previously published key for differentiating third instar larvae of flies of possible forensic importance in Thailand is updated to include this additional species. Some characteristic features of males and females of the species are also provided.